The present invention relates to body implantable prosthesis intended for long-term or permanent fixation in body cavities, and more particularly to the delivery and placement of self-expanding stents.
Self-expanding stents are employed in a variety of patient treatment and diagnostic procedures, for fixation in blood vessels, biliary ducts and other body lumens to maintain the passages. For example, a radially self-expanding stent can be deployed in an artery following a percutaneous transluminal coronary angioplasty (PCTA) or a percutaneous transluminal angio-plasty (PTA) procedure. The stent resists any tendency in the vessel to close, thus countering acute reclosure and plaque restenosis.
A highly preferred construction for a radially self-expanding stent is disclosed in U.S. Pat. No. 4,655,771 (Wallsten), i.e. a flexible tubular braided structure formed of helically wound thread elements. Wallsten discloses a catheter for delivering the stent to the fixation site. Gripping members at opposite ends of the stent initially secure it to the catheter in an axially elongated, reduced radius configuration to enhance delivery. The proximal gripping member is movable distally, initially giving the stent covering the shape of a balloon. In complete deployment, the gripping members release the stent, allowing the stent to assume an axially shortened and radially expanded configuration, in contact with a blood vessel wall or other body tissue.
A similar stent construction is disclosed in U.S. Pat. No. 4,681,110 (Wiktor). A flexible tubular liner is constructed of braided strands of a flexible plastic, and is insertable into the aorta, whereupon it self-expands against an aneurism to direct blood flow past the aneurism. For delivery, the liner is radially compressed within the distal end of a main catheter tube. A secondary tube, inside the main catheter tubing and terminating just proximally of the liner, is held in place while the main tube is withdrawn, thus deploying the liner initially by its distal end.
A prevalent approach to deploying self-expanding stents, often referred to as the "rolling membrane" method, is shown in U.S. Pat. No. 4,732,152 (Wallsten et al). A hose or membrane is folded over upon itself to provide a double wall for maintaining a stent, radially compressed, at the distal end of a catheter or other delivery appliance. When the outer wall is moved proximally, a distal fold likewise travels proximally to expose the stent and allow radial expansion, beginning at the distal end of the stent. As compared to the previously mentioned proximal and distal gripping members, the rolling membrane approach is preferred due to lower cost and increased reliability. There are disadvantages, however, including a lack of one-to-one correspondence between membrane movement and stent exposure, which hinders accurate positioning of the stent. The amount of radial expansion and axial shortening is difficult to predict in view of the uncertainty in lumen size and tissue response to the stent, interfering with accurate stent positioning as stent deployment progresses from one end to the other. This approach requires at least two clinicians or other operators, and does not allow for any reversal in deployment.
Therefore, it is an object to the present invention to provide an apparatus for deploying a radially self-expanding stent, initially only along a medial region of the stent while the axially outward end regions of the stent remain confined in a reduced radius configuration.
Another object of the invention is to provide an apparatus which allows and facilitates deployment of a self-expanding stent by an individual clinician or other user.
A further object is to provide an apparatus and process for deploying radially self-expanding stents in a manner that reduces potential trauma to body tissue.
Yet another object is to provide a process for deploying self-expanding stents that involves interruption and partial reversal of deployment, to facilitate moving the stent axially within a body lumen for more accurate fixation.